It has been proposed that in hypertension changes in vascular wall composition, in vascular wall structure, and in some functions of vascular walls are the effects of increased intravascular pressures. The data supporting these hypotheses have not been confirmed, and therefore the hypotheses need further study. We propose to measure vascular resistance, vascular responses, wall composition, and effects of maximal vasodilation in vessels from normotensive beds of rats with coarctation hypertension. Wall composition of veins will also be measured. If the hypotheses are correct, there should be no evidence for abnormal resistances, responses, effects of maximal vasodilation, and wall composition in these normotensive beds. On the other hand, finding such abnormalities in normotensive beds will suggest that they may play a causative role in hypertension, rather than merely being the effects of the elevated blood presure. The long term goal of the research project is to further describe these abnormalities in ion and water metabolism of blood vessels in hypertension.